[220] During the
mid-1950s, the Air Force contracted with the Rocketdyne Division of
North American Aviation to study rocket engines larger than those in
intercontinental ballistic missiles. This began with the E-1, about
three times larger than an ICBM engine, but Rocketdyne believed that
an engine with a thrust of 4.5 meganewtons (1 million lb)- over six
times larger than an ICBM engine-was feasible. In late 1956, the Air
Force's Scientific Advisory Board was even bolder and recommended
studies of engines up to 22 meganewtons (5 million lb of thrust). The
Air Force, however, believed that such a large thrust was best
attained by clustering smaller engines. In mid-1958, the Air Force
contracted with Rocketdyne for design studies of the F-1 engine, with
a thrust of 4.5 meganewtons. Shortly thereafter, responsibility for
developing a large engine was transferred to NASA; in October, NASA
opened the competition to other contractors and indicated a
preference for 6.7 meganewtons (1.5 million lb of thrust). Rocketdyne
won the competition and a development contract was signed early in
1959.

It was the Army, however, which took the
initiative in proposing large launch vehicles using E-1 and F-1
engines, beginning with studies in the mid-1950s. In late 1957, the
Army missile development tearn, under the technical direction of
Wernher von Braun, submitted a national integrated missile and space
development program to the Department of Defense. Included was a
vehicle with a thrust of 6.7 meganewtons. In early 1958, the National
Advisory Committee for Aeronautics formed a vehicle working group as
part of a space technology committee. The working group was headed by
von Braun and included Abe Silverstein, soon to become the chief
planner at the new civilian space agency. The NACA group modified and
extended the Army's recommended vehicles and propulsion systems. The
favored high-energy propellant combination in both the Army and NACA
plans appeared to be hydrazine-fluorine, a choice influenced by an
Air Force development contract with Bell Aircraft for a small engine
using this combination. In August 1958, the Advanced Research
Projects Agency, responsible for planning and coordinating military
space missions, ordered the Army to devise a development and funding
plan for a large launch vehicle with a first stage using a cluster of
existing ICBM engines; this was later to become Saturn I. NASA's
request for the transfer of both the large vehicle and the Army's
development [221] team met with strong opposition; an agreement in
December 1958 left the Army team intact but responsive to NASA
needs.